Many water pollution problems are being caused by improper disposal of chemicals and/or chemical compounds into ground water reservoirs, streams, lakes and rivers. It is highly desirable that treatment of these contaminated waters be accomplished without the addition of even more chemicals which may result in another form of pollutant or damage to the ecology.
When severe water pollution occurs, one option is to transport the contaminated waste water to an offsite authorized disposal facility. However, transportation of such waste water in most circumstances is prohibitively expensive due to the volumes involved. Furthermore, transportation of waste water deemed hazardous may require prior authorization and permits from regulatory authorities. Rural, residential and agri-business sources of waste water are particularly in need of effective treatment systems.
Since any waste water treatment system that adds chemicals such as chlorine, polyelectrolytes or other flocculates to kill organisms or remove metals and chemicals will necessarily require the production of such materials before use, it is ecologically desirable to provide a purification system which minimizes the requirement for any further manufacture of materials to be used in the treatment process.
The pollution problem posed by the disposal of waste water from domestic and industrial sewage is a serious problem, especially in densely populated areas. In such areas, literally millions of gallons of untreated or inadequately treated waste water from domestic and industrial sewage are discharged into streams, lakes and the like. The discharge of such inadequately treated waste water may cause severe health problems as well as being aesthetically undesirable. A variety of infectious microorganisms are found in municipal waste waters, which, if the water is not disinfected, can lead to outbreaks of gastroenteritis, salmonellosis, typhoid, ear infections and infectious hepatitis.
Chlorine has been traditionally employed for disinfecting water for domestic use and waste water. However, recent reports concerning the carcinogenic effects of chlorinated compounds resulting from chlorine disinfection have stimulated the search for less potentially harmful disinfectants. It has been found that the indiscriminate chlorination of waste waters results in the formation of halogenated compounds which are toxic to aquatic life and potentially toxic to humans. Further, chlorination can satisfy prospective federal water discharge standards only with such high dosages that expensive dechlorination of the treated water is required as a further treatment process step.
Another chemical used for disinfection is sulfur dioxide (SO.sub.2). SO.sub.2 has long been known to the food processing and wine industries for disinfection of equipment and beverages. Although SO.sub.2 has accomplished the disinfection of waste water without the problem of generation of chlorinated carcinogenic compounds, the process has not achieved wide-spread use possibly because of the large quantities of SO.sub.2 required for adequate disinfection.
Purification of polluted water for purposes of reuse, whether starting with agriculture/municipal sewage or with industrial waste, has been concerned primarily with recovery of potable water. Practically speaking, this can be done only after the initial separation and disposal of solid components in an inert state, this being considered a necessary and preliminary step for any subsequent treatment. The solids obtained may then be utilized to a small extent as landfill, but such product was not a primary purpose of the separation. For the most part, the undifferentiated sludge is simply separated in bulk and discarded in the manner most convenient. Purification of the aqueous phase then takes place (if at all) as a successive rather than a concurrent procedure. However, it will be realized that the aqueous run-off from many and probably most water treating procedures (even if only involving flushing) carries a quantity of solid and potentially solid ingredients having tangible economic value if such ingredients could only be recovered in concentrated form without great expense.
Although the discussion thus far has involved water being used for cleaning, whether in the home or in industry, or from run-off, where the introduction of contaminates are obvious, other less obvious forms of contamination are found in examples where a body of water is circulated as a coolant in many industrial chemical plants. Each time this water is returned to the heat exchanger, a part of the water is evaporated and the evaporation step tends to increase the concentration of contained solids merely by reducing the volume of the liquid. However, in the travel through the coolant system, the water typically picks up deposits or sediments from the plumbing system, and in addition, in order to minimize corrosion, foaming and scale formation, various inhibitory additives are mixed into the circulating stream. At some point, the dissolved solid content is built up to a maximum allowable level for continued circulation and it becomes necessary to discard at least part of the fluid mixture and replace it with fresh water. This heavily loaded discard is an illegal pollutant and must be purified before release into flowing streams or the ocean. It would be beneficial if the water could merely be periodically decontaminated and returned to the coolant circulation system.